UPDATE 12/28/13
Free Lego Digital Designer instructions available! Download the latest version of Lego Digital Designer to use the instructions. Download link for the building instructions below. After you open the LDD file:

Click "Building Guide Mode" (F7)

In building guide mode, click Generate HTML building guide (Cmd-T)

With HTML building guide open, skip to the final step (should be step 399) - this is your parts list.

Pieces in red can be in any color you want; they'll be inside the model and won't be seen. Additional parts needed: two rubber bands. One for the trigger and one for the charging handle.